1. Field of the Invention
The present invention relates to an electrode to be used for an electrostatic lens and a method of manufacturing the same as well as to an electrostatic lens and a charged particle beam exposure apparatus using the same.
2. Description of the Related Art
Electron lenses are employed in electron beam exposure apparatus to control the optical characteristics of electron beams. Electron lenses are classified into the electromagnetic type and the electrostatic type. Electron lenses of the electrostatic type are simple in configuration and advantageous for downsizing if compared with electron lenses of the electromagnetic type. On the other hand, multi-beam systems are known for writing patterns simultaneously by means of a plurality of electron beams without using a mask. Electron lens arrays formed by arranging electron lenses one-dimensionally or two-dimensionally are employed in multi-beam systems.
In the field of electron beam exposure technology, realization of electronic optical elements representing little optical aberrations is important because limitations to micro-machining are determined by optical aberrations of electronic optical elements. Japanese Patent Application Laid-Open No. 2007-019194 discloses an electrostatic type lens for charged particle beam formed as high precision assembly by way of a hole etching process of electrostatic lens where a multi-layer structure of apertures and deflection members is formed and through-holes are produced by etching.
An electrostatic type lens for charged particle beam (to be referred to as electrostatic lens hereinafter) has a simple configuration if compared with an electromagnetic type lens as pointed out above. On the other hand, the optical aberrations of an electrostatic lens are highly sensitive to the manufacturing errors of the lens apertures. In particular, when the lens has a round aperture, the astigmatism thereof is highly sensitive to the symmetry of the aperture contour that may be expressed in terms of circularity. Electron beams converged by an aperture that is asymmetric represent astigmatism and higher order aberrations.
In conventional hole etching processes for electrostatic lenses, when forming a through-hole by etching in a state where a multi-layer structure of apertures and deflection members is prepared, the through-hole is formed from a surface of a deflection member to the rear surface in a single etching operation. As the etching operation proceeds from the etching staring surface side, the pattern transfer accuracy falls to degrade the processing accuracy at the etching ending surface. Particularly, when insulating film of SiO2 or the like is employed as etching stop layer, the stop layer becomes electrically charged to warp the ion trajectories of etching gas, which are apt to give rise to a processing error of etching the lateral surface of the hole, a phenomenon referred to as notching. Most advanced deep etching apparatus include those that are equipped with a feature of lessening the charge of the substrate by detecting the processing terminal point, which is referred to as notchingless processing system. However, such apparatus are costly. Furthermore, the inventors of the present invention examined such costly deep etching apparatus and found that they do not provide an effect of satisfactorily suppressing the increase of aberrations due to errors and lack of accuracy in processing lenses for charged particle beam over the entire conductive electrode substrate surface.
In view of the above-identified problems, therefore, an object of the present invention is to provide an electrode of an electrostatic lens that is processed highly accurately and can prevent notching from taking place in a dry etching process, and a method of manufacturing the same.